Is 6 hours of sleep enough for adults

The question is 6 hours of sleep enough for an adult has been evaluated through consensus panels and laboratory investigations. When evaluating nightly rest, researchers contrast subjective feelings of alertness with objective cognitive measures and physiological benchmarks.

Recommendations from the consensus panel

A 2015 joint consensus statement from two sleep-medicine and sleep-research bodies, whose panel of 15 experts used a modified RAND Appropriateness Method to develop a recommendation for adults aged 18 to 60, recommended that adults sleep 7 or more hours per night on a regular basis to promote optimal health. It stated that sleeping less than 7 hours per night on a regular basis is associated with adverse health outcomes, and that sleeping more than 9 hours per night on a regular basis may be appropriate for young adults, people recovering from sleep debt and people who are ill. ^[1]

Cognitive performance after two weeks at six hours in bed

In a 2003 laboratory study of healthy adults aged 21 to 38, one group was limited to 6 hours in bed a night for 14 consecutive days, alongside 4-hour and 8-hour groups and a separate experiment of 3 nights without sleep, 48 participants in total. Restriction to 6 or 4 hours produced cumulative, dose-dependent deficits on all cognitive tasks, and the authors concluded that restriction to 6 hours or less produced cognitive performance deficits equivalent to up to 2 nights of total sleep deprivation. The 6 hours was time in bed, not measured sleep. ^[2]

CIBDOL · Cognitive performance after two weeks at six hours in bed

Differences between reported and measured sleep

In 669 middle-aged adults from a population-based study in Chicago, sleep measured by wrist actigraphy averaged 6 hours while self-reported sleep averaged 6.8 hours, and the correlation between the two was 0.47. The study's model suggested people sleeping 5 hours over-reported by 1.2 hours and people sleeping 7 hours by 0.4 hours. The authors wrote that the true associations between sleep duration and health may differ from those reported using self-reported sleep. ^[3]

Genetic variants identified in natural short sleepers

A 2009 study identified a mutation in the transcriptional repressor DEC2 (hDEC2-P385R) associated with a human short-sleep phenotype. Mice engineered to carry the mutation showed more time awake and less sleep than control mice, in a way that depended on time of day and on sleep deprivation; that part of the work is an animal study. A 2014 paper describes the earlier DEC2 mutation, also called BHLHE41, as causal in a family of short sleepers who needed just 6 hours of sleep per night. ^[4][5]

The 2014 study sequenced the BHLHE41 gene in two cohorts, 200 people who underwent acute sleep deprivation and 217 who underwent chronic partial sleep deprivation. One new variant, Y362H, was found in one twin of a non-identical twin pair and was associated with shorter sleep, less recovery sleep after deprivation and fewer performance lapses during deprivation than the other twin, while both twins had almost identical amounts of non-REM sleep. Another variant the study found had no effect on sleep or on the response to deprivation. ^[5]

A 2019 study, titled as reporting a rare mutation, identified a mutation in the beta1-adrenergic receptor gene in humans who require fewer hours of sleep than most. Mice carrying the same mutation showed short sleep behaviour; that part is an animal study. ^[6]

The documented short-sleep exception rests, in the abstracts cited here, on a family, a single twin pair and carriers of a second rare mutation, with supporting work in mice. None of these abstracts gives a population frequency for the variants; the 2019 paper's title describes its mutation as rare. ^[4][5][6]

This article reports what a consensus statement recommended and what duration studies measured in their samples. It does not set a sleep target for the reader, and anyone concerned about their own sleep should speak to a doctor.